High strength clamps are useful in various industrial applications, typically holding two or more members in place during a procedure of limited duration. For example, a high strength clamp may be used to hold together two structural steel members while the members are welded together. As another example, a high strength clamp may be used to secure heavy equipment to a truck during transport of the equipment from one location to another. As yet another example, a high strength clamp may be used to connect two pipe flanges together while another, more permanent type of fastener is installed or removed, such as bolts, rivets or screws.
One particularly demanding application for high strength clamps is the contingency demating procedure (separation) of aerospace structures, e.g., of the Space Shuttle from either the Russian MIR or the Space Station. This procedure requires a lightweight, high strength and remotely releasable clamping tool for securing the docking module halves of NASA's Orbiter Docking System (ODS) during removal of ninety-six 1/4 inch bolts. The docking module halves define a flanged, circumferential interface sealed by two O-rings, highly loaded, therebetween. Typically, two high strength clamps are placed about 180 degrees apart to hold the interfacing flanges together while the bolts holding them are removed by astronauts. The clamps must have sufficient holding strength and rigidity to oppose the seal and external loads, which can exceed about ten-thousand pounds, and thereby assure the integrity of even the final few remaining bolts and prevent any premature or partial separation of the interfacing flanges. After the removal of the bolts, the astronauts can safely execute the separation by releasing the two clamps, preferable by remote activation under an operating force no greater than 25 pounds. It is also preferred that the clamp jaws open at least 90 degrees upon release to clear the working area and allow for an unobstructed separation of the two flanges.
Cross-sectional side views of a prior art toggle action clamp 10, otherwise known as the Orbiter Docking System 96-bolt contingency clamp, are shown in FIGS. 1 and 2 in the open (released) position and the closed (clamped) position, respectively. This clamp uses a conventional over-center toggle action mechanism 12 with an actuating lever 14 for clamping (FIG. 2) and releasing (FIG. 1) the interfacing flanges 16,18. In order to achieve a low operating force, the clamp gains leverage by incorporating the handle 14 having a substantial assembled length of 32 inches. To further lower the operating force required to release the clamp, the over-center toggle is limited to angles less than one degree (&lt;1). The long linkages 20 of this and other toggle-type clamps are inherently less stiff than other clamp designs and do not maximize the stiffness-to-weight ratio. In fact, this clamp design must be enhanced to achieve the high stiffness and strength necessary for this application, and results in each clamp weighing a substantial 22 pounds.
Another disadvantage of the prior art toggle action clamp is its sensitivity to friction occurring within the joints or pivots 22 of the toggle mechanism. As the axial load in the linkages 20 increases, the frictional forces within the joints 22 that oppose rotation of the linkages increase proportionally, as does the operating force required to release the clamp. Polishing the mating surfaces of linkages decreases the amount of the friction in the joints, but when the linkages are under loads of several thousand pounds, the friction is still significant.
Despite attempts to facilitate release of the prior art clamp 10, release of the clamp still requires an excessive force exceeding the standard 25 pound allowable force for manned space operations. Consequently, an additional winch tool (not shown) must be connected to the end 24 of the long handle 14 in order to release the clamp 10 under such a high load. Using a winch tool further complicates the contingency extravehicular operation for demating of the docking system (represented by flanges 16,18). The clamp also requires certain undesirable maintenance procedures, including calibration and pre-flight checkout.
Therefore, there is a need for a high-performance clamp that provides a high holding force, yet requires only a minimal force to release the clamp. It would be desirable if the clamp could be released by hand, preferably with less than 25 pounds of force. It would also be desirable if the clamp could open fully during release to allow easy separation of the clamped objects. It would be further desirable if the clamp were both lightweight and compact. It will be understood by those in the art that such characteristics are of importance and benefit in various ground-based applications of such clamps, in addition to the context of the illustrative aerospace example just described.